An estimated twenty-five percent of homes in Missouri rely on an onsite wastewater treatment system (OWTS) in areas where public sewers are not available. Onsite systems
treat wastewater and disperse it on the property where it is generated. When functioning properly, onsite systems prevent human contact with sewage, and prevent contamination
of surface and groundwater. Factors that affect the proper functioning of onsite systems include the site and soil conditions, design, installation, operation and maintenance.

The Missouri Department of Health and Senior Services (DHSS) has set minimum state standards for OWTS. These standards cover new systems and major changes to existing systems.
Some examples of major changes are replacing a sewage tank, and replacing or expanding an absorption field. These standards became effective in January 1996.

Generally, a permit must be obtained before starting construction or repair work. However, certain residential properties may be exempt from state permitting requirements.
When authority is based on a local ordinance, regulation can be more restrictive than the state standard; check with your local authority. In most counties, the local health
department issues OWTS construction permits. In the other counties the authority is another agency, such as a sewer district, building department, or planning and zoning
department.

Public health and the environment are protected when new systems are constructed, and failing systems are repaired or replaced, using criteria equal to or better than
Missouri's Minimum Construction Standards. Homeowner understanding of the need for regular maintenance and proper operation of their onsite sewage system is important for
long-term system performance and public health protection.